Magnetic recording medium, a manufacturing method thereof, and a magnetic recording unit using thereof

ABSTRACT

A magnetic recording medium comprising a substrate  1 , an inorganic compound layer  2  which works as a shielding layer, a magnetic layer  3  and a protective layer  4  which are laminated on said substrate; wherein said inorganic compound layer  2  comprises column-like crystal particles  6  and amorphous grain boundary phases isolating said particles  6,  wherein said magnetic layer  3  has magnetic particles  14  arranged regularly and epitaxially grows on said inorganic compound layer  2,  and wherein the grain sizes and the standard grain size deviation of magnetic particles  14  of said magnetic layer  3  reflect those of said inorganic compound layer  2.

BACKGROUND OF THE OF THE INVENTION

[0001] This invention relates to a high-performance and high-reliabilitymagnetic recording medium, a method thereof, and a magnetic recordingunit using thereof.

[0002] Japanese Laid-open Patent Publication No. 10-177712 (1998) hasdisclosed a magnetic recording medium comprising a glass substrate, afirst under layer comprising tantalum (Ta) and boron (B), a second underlayer mainly comprising chromium (Cr), and a magnetic layer which arelaminated on said substrate; wherein said first under layer works toadjust sizes of grains in the second ground and magnetic layers, andsaid ground and magnetic layers are formed with the fine crystals ofsaid first under layer directly reflected upon them. This invention ischaracterized by high coercive force and low noises.

[0003] Japanese Laid-open Patent Publication No. 6-259743 (1994) hasdisclosed a magnetic recording medium comprising a non-magneticsubstrate, a second under layer having sodium chloride (NaCl) typecrystal structure, a first under layer having a body-centered cubicstructure, and a magnetic layer having a hexagonal close-packedstructure which are laminated on said substrate. This invention ischaracterized by improved crystal orientation of the magnetic layers.

[0004] Japanese Laid-open Patent Publication No. 7-311929 (1995) hasdisclosed a magnetic recording medium having a thin magnetic layer on aNiP under layer wherein crystal particles in said magnetic layer areisolated from each other by a crystal grain boundary containingnon-ferromagnetic non-metallic phase. This invention is characterized byhigh coercive force and low noises.

[0005] Japanese Laid-open Patent Publication No. 11-66533 (1999) hasdisclosed a magnetic recording medium forming a thin magnetic layer on anon-magnetic under layer made of one or more of metals Cr, Pt, Ta, Ni,Ti, Ag, Cu, Al, Au, W, Mo, Nb, V, Zr, and Zn; wherein lots of magneticparticles in said magnetic layer are isolated from each other by grainboundary comprising the same components as the magnetic particles. Thisinvention is characterized by high coercive force and low noises.

SUMMARY OF THE INVENTION

[0006] However, the aforesaid conventional technologies have limitationson control of distributions of sizes of crystal particles in a magneticlayer constituting the magnetic recording disk medium. Therefore, themagnetic layer cannot be free from containing both fine and largeparticles. Information recorded on such magnetic layers would beaffected and disturbed by magnetic fields (noises) leaking fromsurrounding larger particles or mutual actions of large particles. Suchnoises are enemies to super-high density recording of 20 Gbit/inch² orabove.

[0007] One object of the present invention is to provide a magneticrecording medium fit for stable high-density recording and a methodthereof.

[0008] Another object of the present invention is to provide a magneticrecording unit using said magnetic recording medium.

[0009] We inventors discovered that the sizes and distribution (oruniformity of grain sizes) of crystal particles in an inorganic compoundlayer are very dependent upon the sizes and distribution of a magneticlayer by growing the magnetic layer on the inorganic compound layerwhich comprises crystal particles and amorphous grain boundary phasesurrounding the crystal particles.

[0010] Further we discovered that we could obtain a stable high-densityrecording magnetic layer having fine magnetic particles of almost anidentical size arranged regularly by narrowing the grain sizedistribution of the crystal particles in the inorganic compound layer,that is, controlling to have fine and uniform sizes of the crystalparticles in the inorganic compound layer.

[0011] Further, we discovered that, for a magnetic layer comprisingcrystal magnetic particles and deposits (a grain boundary phase) formedaround the magnetic particles, the magnetic particles of the magneticlayer are finer and their grain sizes are uniform.

[0012] Furthermore, an intermediate layer can be provided between theinorganic compound layer and the magnetic layer. We discovered that wecould control the particular structure of the magnetic layer bycontrolling the size and distribution of the crystal particles of theintermediate layer. Particularly, when a magnetic layer comprisescrystal magnetic particles and deposits (a grain boundary phase) formedaround the magnetic particles, we discovered that the magnetic particlesof the magnetic layer were finer and their grain sizes were uniform.Below will be explained the summary of the present invention.

[0013] (1) A magnetic recording medium comprising a substrate and aplurality of information-recording magnetic layers laminated on saidsubstrate, further comprising an inorganic compound layer containingcrystal particles and amorphous grain boundary phases surrounding saidparticles between said substrate and said magnetic layers; wherein

[0014] said magnetic layers contains crystal magnetic particles whosemean grain size is 4 nm to 15 nm and the standard deviation of the grainsize (σ) is 25% or less of said mean grain size.

[0015] (2) Said magnetic layers are on said magnetic recording mediumcomprising crystal magnetic particles and an amorphous grain boundaryphase surrounding said magnetic particles.

[0016] (3) Said inorganic compound layer comprises a first componentcontaining sodium chloride (NaCl) or spinel type crystal oxide and asecond component containing oxide, nitride, or boride of elementsbelonging to Groups I to V of the periodic table. Said particles andsaid grain boundary phase contain both the first and second componentsand said particles contain more first component than said grain boundaryphase.

[0017] The inorganic compound layer fit for the magnetic recordingmedium according to the present invention contains

[0018] (a) a first component comprising sodium chloride (NaCl) or spineltype crystal oxide and

[0019] (b) a second component comprising at least one of oxide, nitride,and boride of elements belonging to Groups I to V of the periodic table.

[0020] An oxide having the sodium chloride (NaCl) type crystal structurecan be one selected from a group of cobalt oxide (CoO), ferric oxide(Fe₂O₃), magnesium oxide, manganese oxide, titanium oxide, copper oxideor nickel oxide.

[0021] Similarly, a spinel type crystal oxide can be selected fromcobalt oxide (Co₃O₄) or ferrous oxide (Fe₃O₄).

[0022] Said crystal particle of the inorganic compound layer contains65% to 98% by weight of oxide (a) and 35% to 2% by weight of oxide (b)and said grain boundary phase contains 50% to 90% by weight of oxide (a)and 50% to 10% by weight of oxide (b). Both the crystal particles andthe grain bound a ryphase preferentially contain oxides (a) and (b).Further, the crystal particle of the inorganic compound layer shouldalways contain greater oxide (a) than the grain boundary phase. Here,the mean grain size, the standard deviation (σ) of grain size, the shortdiameter to long diameter ratio of said particle, and the grain boundaryphase width should be respectively 4 nm to 15 nm, 25% or less of saidmean grain size, 0.7 to 1.0 and 0.1 nm to 2 nm in that order.

[0023] The magnetic layer formed on the inorganic compound layer is aferromagnetic layer which is an alloy of cobalt (Co) as a maincomponent, platinum (Pt), and at least one selected from a group ofelements chrome (Cr), tantalum (Ta), and niobium (Nb). Thisferromagnetic layer has a structure in which at least one of chrome(Cr), tantalum (Ta), and niobium (Nb) is deposited between the crystalparticles mainly comprising cobalt (Co) and other crystal particles.

[0024] The sizes and size distribution of magnetic particles in themagnetic layer are approximately equal to those of the inorganiccompound layer due to the particle structure of the inorganic compoundlayer reflect the magnetic particles in the magnetic layer. Therefore,the magnetic layer can have fine magnetic particles of uniform sizes.

[0025] At least one of oxide, nitride, and boride of elements belongingto Groups I to V of the periodic table can be deposited on the boundaryof the magnetic particles. In this case, the sizes and size distributionof magnetic particles in the magnetic layer are approximately equal tothose of the inorganic compound layer. The mean grain size, the shortdiameter to long diameter ratio of said particle, and the standarddeviation (σ) of grain size are respectively 4 nm to 15 nm, 0.7 to 1.0,and 25% or less of said mean grain size in that order.

[0026] If the difference between lattice constants of the crystal of themagnetic particles of the magnetic layer and the particles of theinorganic compound layer is ±10% or under, the sizes and sizedistribution of magnetic particles in the magnetic layer become closerto those of the inorganic compound layer.

[0027] The intermediate layer between the inorganic compound layer andthe magnetic layer uses a chrome-related metal layer. The sizes and sizedistribution of metal particles in the intermediate layer reflect theparticle structure of the inorganic compound layer and the sizes andsize distribution of magnetic particles in magnetic layer reflect theparticle structure of metal particles of the inorganic compound layer.In other words, the sizes and size distribution of magnetic particles inthe magnetic layer are approximately equal to those of the inorganiccompound layer and we can obtain a magnetic layer of fine particles ofuniform sizes.

[0028] At least one of oxide, nitride, and boride of elements belongingto Groups I to V of the periodic table can be deposited on the boundaryof the Cr-related metal particles of the intermediate layer. In thiscase, the sizes and size distribution of magnetic particles in themagnetic layer becomes closer to those of the inorganic compound layer.

BRIEF DESCRIPTION OF DRAWINGS

[0029]FIG. 1 is a schematic sectional diagram of a magnetic recordingmedium which is a first embodiment of the present invention; FIG. 2 is aTEM picture showing a typical structure of the inorganic compound layer;FIG. 3 is a perspective view of a magnetic recording unit; and FIG. 4shows schematic sectional diagrams of magnetic recording media ofEmbodiment 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Manufacturing Method

[0030] Below will be explained a method of forming an inorganic compoundlayer on a substrate in accordance with the present invention. Thismethod sputters the following two targets (a) and (b) simultaneously orsputters a mixture of these two targets (a) and (b):

[0031] (a) target comprising oxide of the sodium chloride (NaCl) orspinel type crystal structure;

[0032] (b) Target comprising at least one of oxide, nitride, and borideof elements belonging to Groups I to V of the periodic table.

[0033] To form said magnetic layer on the inorganic compound layer, thismethod simultaneously sputters

[0034] a first target comprising cobalt (Co) as a main component,platinum (Pt) and at least one of chromium (Cr), tantalum (Ta), andniobium (Nb), and

[0035] a second target comprising at least one of oxide, nitride, andboride of elements belonging to Groups I to V of the periodic table orsputters a mixture of these two targets.

[0036] In this case, it is preferable to control the mixture ratio ofthe target materials so that the material may contain 65% to 98% byweight of an oxide which is the first component and 35% to 2% by weightof oxide, nitride, or boride which is the second component.

[0037] By sputtering, magnetic particles of the magnetic layerepitaxially grow on the crystal particles of the inorganic compoundlayer. The resulting magnetic layer has fine particles of uniform grainsizes.

[0038] To form a chrome-related intermediate metal layer on theinorganic compound layer, this method simultaneously sputters a firsttarget mainly comprising chrome (Cr) and a second target comprising atleast one of oxide, nitride, and boride of elements belonging to GroupsI to V of the periodic table or sputters a mixture of these two targetmaterials.

[0039] In this case, it is preferable to control the mixture ratio ofthe targets so that the material may contain 65% to 98% by weight of anoxide which is the first component and 35% to 2% by weight of oxide,nitride, or boride which is the second component.

[0040] By sputtering, crystal particles of the intermediate layerepitaxially grow on the crystal particles of the inorganic compoundlayer. The resulting intermediate layer has fine particles of uniformgrain sizes. By forming a magnetic layer on this intermediate layer bysputtering as explained above, magnetic particles of the magnetic layerepitaxially grow on the crystal particles of the intermediate layer. Theresulting magnetic layer has fine particles of uniform grain sizes.

[0041] For smooth growth of magnetic particles, size and distribution,it is preferable that the structure of crystal particles of theinorganic compound layer or the intermediate layer is equal or similarto the structure of the magnetic particles of the magnetic layer.

[0042] The above term “similar to” means that the difference between thelattice constant of the magnetic particles of the magnetic layer and thelattice constant of the crystal particles of the inorganic compoundlayer and the intermediate layer is ±10% or under, more preferably ±5%or under for smooth growth of crystals.

[0043] The resulting fine magnetic particles of uniform sizes in themagnetic layer can reduce noises, thermal fluctuation, thermaldemagnetization, and the unit of inversion of magnetism. This is fit forhigh-density recording.

[0044] For example, the mean grain size, the short diameter to longdiameter ratio, and the standard deviation (σ) of grain size of magneticparticles in the magnetic layer are respectively 4 nm to 15 nm, 0.7 to1.0, 25% or less of said mean grain size in that order. This enableshigh-density recording of a coercive force of 3000 Oe or more, the unitof inversion of magnetism of 100 nm or under, and a density of 20Gbit/inch² or above.

[0045] The unit of inversion of magnetism indicates how many magneticparticles in the magnetic layer are recorded or erased assuming that theminimum inversion unit is one magnetic particle of the magnetic layer.This can be determined by the use of a magnetic force microscope (MFM).

Embodiment 1

[0046]FIG. 1 shows a cross-sectional view of a magnetic recording mediumwhich is one embodiment of the present invention. The magnetic recordingmedium 5 comprises a substrate 1, an inorganic compound layer 2 whichworks as a shielding layer, a magnetic layer 3 which records informationand a protective layer 4. These layers are formed on the substrate inthat order. The inorganic compound layer 2 comprises column-like crystalparticles 6 and amorphous grain boundary phases 7 which isolateparticles 6 each others. The magnetic layer 3 comprises magneticparticles in arrangement. This invention terms a boundary betweenparticles a grain bondary phase and a thick boundary having amorphousmaterials a grain boundary phase 7. The magnetic layer 3 of FIG. 1 has agrain bondary phase 15 between the magnetic particles 14.

[0047] This embodiment uses a 2.5′-diameter glass substrate on which aninorganic compound layer 2 of 30 nm thick is formed by simultaneoussputtering of a sintered target of cobalt oxide CoO and another sinteredtarget of 2 molar parts of silicon oxide SiO₂ and 1 molar part oftitanium oxide TiO₂.

[0048] The sputtering condition is pure argon (Ar) gas as a discharginggas for sputtering, discharging gas pressure of 2 mTorr, high-frequencypower supply of 100 W to 1000 W/mm diameter at the cobalt oxide side,and high-frequency power supply of 100 W to 1000 W/mm diameter at thesilicon oxide (SiO₂) titanium oxide (TiO₂) side.

[0049] The preferential thickness of the inorganic compound layer 2 is 5nm to 50 nm. If the thickness of the inorganic compound layer 2 isthinner than 5 nm, the inorganic compound layer 2 is directly affectedby the surface structure of the substrate and cannot fully show itscharacteristics. As the thicker inorganic compound layer can fully showthe characteristics of the inorganic compound layer, the layer thickness5 nm to 50 nm is enough for a under layer of the recording medium.

[0050] Table 1 shows the relationship of target, supply powers,components and characteristics of the resulting inorganic compoundlayer, and the validity of the obtained crystals. TABLE 1 Components ofthe inorganic Inorganic compound layer Target and supply compound layer(wt %) Standard deviation/ Mean Short power (W) Crystal Grain Mean grainMean grain diameter/ Crystal No. CoO SiO2—TiO₂ particle boundary size(nm) size × 100 (%) Long diameter ratio status Remarks 1 100 100 CoO: 85CoO: 80 8.3 14.2 0.90 ◯ — SiO₂ + TiO₂: 15 SiO₂ + TiO₂: 20 2 200 100 CoO:88 CoO: 78 8.6 12.3 0.92 ◯ — SiO₂ + TiO₂: 12 SiO₂ + TiO₂: 22 3 300 100CoO: 93 CoO: 75 9 11.2 0.93 ◯ — SiO₂ + TiO₂: 7 SiO₂ + TiO₂: 25 4 500 100CoO: 95 CoO: 73 9.2 13.2 0.92 ◯ — SiO₂ + TiO₂: 5 SiO₂ + TiO₂: 27 5 700100 CoO: 98 CoO: 83 14.2 17.5 0.91 ◯ — SiO₂ + TiO₂: 2 SiO₂ + TiO₂: 17 61000  100 CoO: 99.5 CoO: 90 18.6 25.6 0.65 ◯ Comparative SiO₂ + TiO₂:0.5 SiO₂ + TiO₂: 10 example 7 200 400 CoO: 80 CoO: 53 8.1 12.8 0.89 ◯ —SiO₂ + TiO₂: 20 SiO₂ + TiO₂: 47 8 200 800 CoO: 78 CoO: 50 7.2 18.6 0.88◯ — SiO₂ + TiO₂: 22 SiO₂ + TiO₂: 50 9 200 1000 CoO: 65 CoO: 50 6.2 21.20.89 ◯ — SiO₂ + TiO₂: 35 SiO₂ + TiO₂: 50 10 170 1000 CoO: 63 CoO: 45 — —— X Comparative SiO₂ + TiO₂: 37 SiO₂ + TiO₂: 55 example 11 300 0 CoO:100 — 20.3 26.1 0.60 ◯ Comparative example

[0051] Each of the resulting inorganic compound layers has particles 6containing cobalt oxide dispersed in the layer. The particles 6 areoxides of the NaCl type crystal structure. Inorganic compound layers No.1 to No. 5 and No. 7 to No. 9 have grain boundary phases 7 in the grainboundary but inorganic compound layers No. 6 and No. 11 have no grainboundary phase. Particles in inorganic compound layer No. 10 are notfully crystallized. Particles and grain bondary phases are hard to bedistinguished from each other.

[0052] Inorganic compound layer No. 1 to No. 9 and No. 11 have goodcrystal particles 6. The mean grain size and the “Standard deviation(σ)/grain size×100” value of the inorganic compound layers except forNo. 6 and No. 11 are respectively 15 nm or under and 25% or under. Themean grain size and the “Standard deviation (c)/grain size×100” value ofinorganic compound layer 10 cannot be evaluated because its particlesand grain bondary phases are hard to be distinguished from each other asexplained above.

[0053] As seen from inorganic compound layers No. 6, No. 10, and No. 11,when the CoO component and the mixture of SiO₂ and TiO₂ components arenot in the recommended ranges 65% to 98% by weight and 35% to 2% byweight respectively, particles 6 become less crystallized and thestandard deviation (σ) of grain size of the particles becomes greater.This destroys the characteristics of the inorganic compound layers.

[0054]FIG. 2 shows the top magnified view of the surface of inorganiccompound layer 3 (by a transparent electron microscope (TEM)). As seenfrom this figure, particles 6 of the mean grain size of 9 nm aredisposed regularly in rows and in lines. As the result of TEMobservation of the surfaces of the other inorganic compound layers, theparticles 6 of the inorganic compound layers disposed regularly atspaces of 0.1 to 2 nm (which is the width of the grain boundary phase).

[0055] The mean diameter (size) of particles 6 is estimated by measuringthe area of a TEM photo square containing about 300 particles (see FIG.2) and dividing the area by the number of particles assuming that theparticles are all circles. Further, we observed lattice images in theparticles 6. Therefore, the particles are assumed to be crystal.However, the grain boundary phase 7 has no lattice image and is assumedto be amorphous.

[0056] We used the EDX (Energy-Dispersed Characteristic X-Ray Analyzer)of the FE-TEM (Field Emission Type Transparent Electron Microscope) tomeasure the compositions of the particles 6 and the grain boundaryphases 7. The beam diameters for the particles 6 and the grain boundaryphases 7 are respectively about 5 nm (for 6) and about 0.5 nm (for 7).

[0057] The particles 6 of inorganic compound layer 3 contained 93% byweight of cobalt oxide having the NaCl type crystal structure and 7% byweight of the other oxides SiO₂ and TiO₂. Similarly, the grain boundaryphases 7 contained 75% by weight of cobalt oxide and 25% by weight ofthe other oxides SiO₂ and TiO₂. As the result of similar analyses of theother inorganic compound layers, we found that the particles of theinorganic compound layers (except for the comparative examples)contained 65% to 98% by weight of cobalt oxide CoO and the grainboundary phases contained 50% to 90% by weight of cobalt oxide CoO. Theother components were SiO₂ and TiO₂. Judging from the grain sizedistribution of particles 6, we found that all inorganic compound layersexcept for No. 6, No. 10, and No. 11 have a “Standard deviation(σ)/grain size×100” value of 25% or under and their sizes (diameters)are uniform.

[0058] Next, we formed a magnetic layer 3 of 12 nm thick comprising 69%atomic weight cobalt (Co), 19% atomic weight chrome (Cr) and 12% atomicweight platinum (Pt) on each of the inorganic compound layers 2 (No. 1to No. 11 in Table 1) by sputtering, using a Co—Cr—Pt alloy as asputtering target and pure argon as a discharging gas. The discharginggas pressure was 3 mTorr and the supply d.c. power is 300 W/100 mmdiameter.

[0059] Next, we formed a carbon protective layer 4 of 5 nm thick on themagnetic layer 3, using pure argon as a discharging gas. The discharginggas pressure was 5 mTorr and the supply d.c. power is 800 W/100 mmdiameter. Argon gas used in this embodiment can be substituted by a gascontaining nitrogen to make the protective layer 4 closer and tighter.

[0060] From close observation of surfaces and sections of the magneticlayers 3 formed on the inorganic compound layers 2 except for No. 10 inTable 1 through the electron microscope, we found epitaxial growth ofparticles on the inorganic compound layer 2 and also found that theparticles 6 of the inorganic compound layers are approximately as big asthe magnetic particles 14 of the magnetic layer 3.

[0061] From the grain size distribution of magnetic particles 14, wefound that the “Standard deviation (σ)/grain size ×100” values ofinorganic compound layers except for No. 6, No. 10, and No. 11 in Table1 are 25% or under and that the grain sizes (diameters) are uniform.This is because the magnetic particles 14 in the magnetic layer 3 areaffected by the grain sizes and the standard deviation of particles inthe inorganic compound layers.

[0062] As the result of measurement of magnetic characteristics of themagnetic layer 3, we found that the coercive forces of the inorganiccompound layers except for No. 6, No. 10, and No. 11 are 3.0 to 3.8 kOe.Their coercive rectangular ratio S* which is an index of a rectangularhysteresis in the Magnetic Hysteresis loop (M-H loop) (a curveindicating the transition of magnetization M when a magnetic fieldstrength H is applied to a ferromagnetic material) is 0.75 to 0.88. Thismeans that the magnetic layers have excellent magnetic characteristics.This is assumed that the diameters of the magnetic particles 14 of themagnetic layers 3 are small and uniform. Contrarily, the coercive forcesof the magnetic layers formed on the inorganic compound layers No. 6,No. 10, and No. 11 were 2 to 2.5 Oe.

[0063] As explained above, the magnetic layers formed on the inorganiccompound layers No. 6, No. 10, and No. 11 in Table 1 contain particleswhose standard deviation of grain sizes is big because the particles ofthe magnetic layers on the inorganic compound layers are not fullycrystallized and their standard deviation of grain sizes is very big.Therefore the magnetic characteristics of the magnetic layer areinferior.

[0064] Then we applied a lubricant to the surface of the protectivelayer 4, assembled the resulting magnetic recording medium 5 in amagnetic recording/playing unit, and evaluated the recording and playingcharacteristics of the magnetic recording medium. FIG. 3 shows anexternal view of the magnetic recording/playing unit.

[0065] The magnetic recording/playing unit comprises a plurality ofmagnetic recording media 5, a media rotating means 8, and a drive unit 9for driving read/write head units.

[0066] The read/write head unit 10 has a play head and a recording head.The recording head comprises an upper magnetic core, a lower magneticcore, and a gap layer. The gap film of the recording head is a softmagnetic layer having high-saturation magnetic flux density of 2.1 T andthe gap length is 0.15 μm. The playing head comprises a magnetic headhaving an enormous magnetic resistance effect.

[0067] There is an aerial distance of 20 nm between the magnetic layerof the magnetic recording medium 5 and the surface of the magnetic headfacing to the magnetic layer. We wrote a signal equivalent to 20Gbit/inch² on the magnetic recording medium 5 and evaluated its S/Ncharacteristics. The magnetic layers 3 of the inorganic compound layersexcept for No. 6, No. 10, and No. 11 in Table 1 had reproduction outputsof 27 dB to 36 dB. Contrarily, the magnetic layers 3 of the inorganiccompound layers No. 6, No. 10, and No. 11 in Table 1 had reproductionoutputs of 17 dB to 19 dB.

[0068] As the result of measurement of the inversion-of-magnetizationunits of the magnetic layers by the magnetic force microscope (MFM), wefound that the units for the magnetic layers formed on inorganiccompound layers except for No. 6, No. 10, and No. 11 in Table 1 are 4 to5 magnetic particles (14) and small enough.

[0069] As the result of measurement of the width of a zigzag patternexisting in the magnetization transition area of eack track on themagnetic recording medium 5 by the magnetic force microscope (MFM), wefound that the width is 0.1 μm which is much shorter than the gap lengthof the recording head. We also found generation of no demagnetizationdue to heat and thermal fluctuation.

[0070] This is because the magnetic particles 14 of the magnetic layers3 have uniform sizes (diameters) and the magnetic interaction ofmagnetic particles 14 is reduced. It is preferential that the width ofthe zigzag pattern is smaller than the gap length over the whole tracks,which is not required. This can strikingly reduce noises of the magneticrecording medium.

[0071] Further, as the widths of zigzag patterns on the magneticrecording medium in accordance with the present invention are smallerthan those of the conventional magnetic recording medium, the tracks canbe packed more closely, which enables super-high density recording of 20Gbit/inch² or above.

[0072] Although this embodiment uses glass substrates as substrate 1,they can be substituted by aluminum substrates, aluminum alloysubstrates, or plastic resin substrates. It is also possible to changesubstrate sizes. Further, additional layers such as a NiP or Co—Cr—Zrlayer can be formed on the substrates to improve the surfacecharacteristics of the substrates.

[0073] It is possible to use a target comprising cobalt (Co) as amaincomponent, platinum (Pt), at least one of chromium (Cr), tantalum (Ta),and niobium (Nb), and other elements as the components of the magneticparticles in the magnetic layer.

Embodiment 2

[0074] This embodiment used targets No. 1 to No. 10 in Table 2 to forminorganic compound layers 2 of FIG. 1. Target No. 1 is a sintered targetof NiO, FeO, MgO, TiO, MnO, Co₃O₄, Fe₃O₄, or any selected from a groupof these oxides and target No. 2 is molten soda lime glass(Na₂O—SiO₂—CaO). TABLE 2 Inorganic compound layer Magnetic layerComponents of the inorganic Mean Standard Mean Standard Target andsupply compound layer (wt %) grain deviation/ grain deviation/ power (W)Crystal Grain size Mean grain size Mean grain No. Target 1 Target 2particle boundary (nm) size × 100 (%) (nm) size × 100 (%) Remarks 1 NiO300W — NiO: 100 — 2.3 25.3 21 29 Comparative example 2 Nio 300W Sodalime NiO: 88 NiO: 78 12.3 16.1 12.2 16.1 — glass 100W Glass Glasscomponent: 12 component: 22 3 FeO 300W Soda lime FeO: 83 FeO: 73 11.516.3 11.7 15.9 — glass 100W Glass Glass component: 17 component: 27 4FeO + CoO Soda lime CoO + FeO: 85 CoO + FeO: 75 10.5 17.4 10.3 18 —glass 100W Glass Glass component: 15 component: 25 5 MgO 300W Soda limeMgO: 87 MgO: 80 12.4 10.6 11.7 13.2 — glass 100W Glass Glass component:13 component: 20 6 TiO 300W Soda lime Tio: 89 Tio: 69 13.2 9.2 11.2 16.9— glass 100W Glass Glass component: 11 component: 31 7 MnO 300W Sodalime MnO: 91 MnO: 81 11.5 20.1 14.2 13.9 — glass 100W component: 9component: 19 8 CoO + Soda lime CoO + NiO + TiO: 89 CoO + NiO + TiO: 7913.2 12.8 12.9 14.4 — NiO + glass 100W Glass Glass TiO 300W component:11 component: 21 9 Co₃O₄ Soda lime Co₃O₄: 82 Co₃O₄: 72 6.5 15 7.2 17 —300W glass 100W Glass Glass component: 18 component: 28 10 Fe₃O₄ 300WSoda lime Fe₃O₄: 85 Fe₃O₄: 75 8.3 16.5 8.6 17.6 — glass 100W Glass Glasscomponent: 15 component: 25

[0075] As the result of microscope observation of the surfaces ofinorganic compound layers 2, we found that the inorganic compound layersNo. 1 to No. 8 have particles 6 of oxides of the NaCl type crystalstructure dispersed and the inorganic compound layers No. 9 to No. 10have particles 6 of oxides of the spinel crystal structure dispersed.

[0076] The mean grain size, the short diameter to long diameter ratio,and the standard deviation (σ) of grain size of particles 6 of theinorganic compound layers No. 2 to No. 10 were respectively 6.5 nm to13.2 nm, 0.7 to 1.0, 9.2% to 20.1% of said mean grain size in thatorder. The mean grain size and the standard deviation (σ) of grain sizeof particles in the inorganic compound layer No. 1 were respectively 23nm and over 25%.

[0077] We recognized grain boundary phases 7 having amorphous oxidesaround particles 6 in the inorganic compound layers No. 2 to No. 10 butno clear grain boundary phase in the inorganic compound layer No. 1.

[0078] Therefore, magnetic particles in a magnetic layer 3 formed oneach of the inorganic compound layers No. 2 to No. 10 in Table 2 reflectthe grain sizes and the standard deviation characteristics of theinorganic compound layers 2.

[0079] However, this is not reflected upon the magnetic layer of theinorganic compound layer No. 1. As the result, the grain size of themagnetic particles was 15 nm or above and the standard deviation (σ) inthe grain size distribution exceeded 25%. Therefore, inorganic compoundlayers No. 2 to No. 10 are preferable for high-density recording of 20Gbit/inch² or above.

[0080] As explained above, we can prepare a magnetic recording mediumfit for high-density recording by using crystal particles 6 containingoxides of NaCi or spinel type crystal structure and an inorganiccompound layer comprising amorphous grain boundary phases.

Embodiment 3

[0081] This embodiment formed an inorganic compound layer 2 of 30 nmthick on a substrate 1 of FIG. 1 by sputtering a target comprisingcobalt oxide CoO and a target comprising soda lime glass (SiO₂—Na₂O—CaO)to which Si₃N₄, TiN, Fe₂B or CoB is added.

[0082] The sputtering condition was pure argon (Ar) gas as a discharginggas for sputtering, discharging gas pressure of 2 mTorr, high-frequencypower supply of 300 W/mm diameter at the cobalt oxide side, andhigh-frequency power supply of 200 W/mm diameter at the soda lime glassside.

[0083] We heated the substrate at 300 degrees C. during growth oflayers. As the result of TEM observation of the surface of eachinorganic compound layer, we found that the mean grain size and theshort diameter to long diameter ratio were respectively 9.8 nm to 12.5nm, 0.7 to 1.0 and that each crystal particle is wrapped with anamorphous grain boundary phase. We also found that the particles arecrystallized and the standard deviation (σ) of the grain size in thegrain size distribution is 11.9% to 20.1% of the mean grain size.

[0084] The grain boundary phase contained SiO₂, NaO₂, CaO and theadditional component of Si₃N₄, TiN, Fe₂B, or CoB. The grain boundaryphase is 0.5 nm to 1.0 nm thick and can be made thicker by adding Si₃N₄,TiN, Fe₂B or CoB to the target.

Embodiment 4

[0085] This embodiment prepared magnetic recording media No. 1 to No. 7(see Table 3) using substrates 1 on which an inorganic compound layer 2is formed under the same condition of No. 3 of Embodiment 1. TABLE 3Intermediate layer Magnetic layer Mean Standard Mean Standard Target forgrain deviation/ Lattice grain deviation/ intermediate layer size Meangrain con- Target for magnetic layer size Mean grain No. Target 1 Target2 (nm) size × 100 (%) stant ( ) Target 1 Target 2 (nm) size × 100 (%)Remarks 1 Cr100 — 10.5 20.1 2.9244 Co69Cr19Pt12 — 10.5 20.6 FIG. 4 (a)(Cr: 100 at %) (Co:69 at %, Cr.19 at %, PT::12 at %) 300W 2 Cr90Ti10 —12.3 18.1 2.9606 Co69Cr19Pt12 — 10.3 19.5 (Cr: 90 at %, (Co:69 at %, Ti:10 at %) Cr.19 at %, 300W PT::12 at %) 300W 3 Cr80Ti20 — 11.5 17.92.9964 Co69Cr19Pt12 — 11.5 18.3 (Cr: 80 at % (Co:69 at %, Ti: 20 at %)Cr.19 at %, 300W PT::12 at %) 300W 4 Cr70Ti30 — 11.2 17.3 3.0297Co69Cr19Pt12 — 10.8 18.2 (Cr: 70 at % (Co:69 at %, Ti: 30 at %) Cr.19 at%, 300W PT::12 at %) 300W 5 Cr90Ti10 SiO₂ + TiO₂ 10.5 14.9 —Co69Cr19Pt12 — 10.3 14.6 FIG. 4 (b) (Cr: 90 at % (SiO₂: TiO₂ = 1:1(Co:69 at %, Ti: 10 at %) 100W Cr.19 at %, 300W PT::12 at %) 300W 6Cr90Ti10 SiO₂ + TiO₂ 10.5 14.9 — Co69Cr19Pt12 SiO₂ + TiO₂ 10.5 13.4 FIG.4 (c) (Cr: 90 at % (SiO₂: TiO₂ = 1:1 (Co:69 at %, (SiO₂: TiO₂ = 1:1 Ti:10 at %) 100W Cr.19 at %, 100W 300W PT::12 at %) 300W 7 A magnetic layeris directly formed on the inorganic Co69Cr19Pt12 SiO₂ + TiO₂ 10.8 15.4FIG. 4 (d) compound layer without the intermediate layer. (Co:69 at %,(SiO₂: TiO₂ = 1:1 Cr.19 at %, 100W PT::12 at %) 300W

[0086] an intermediate layer 4 on the inorganic compound layer 2. Theseintermediate layers have different Cr and Ti compositions. Eachintermediate layer has a magnetic layer 3 on it. FIG. 4(a) shows aschematic sectional view of the magnetic recording medium No. 1.

[0087] We formed an intermediate layer of 10 nm thick by sputtering aCr—Ti alloy target; using pure argon as the discharging gas. Thedischarging gas pressure is 3 mTorr and the supply d.c. power is 800W/100 mm diameter.

[0088] Similarly, we formed a magnetic layer of 12 nm thick bysputtering a Co—Cr—Pt alloy target, using pure argon as the discharginggas. The discharging gas pressure is 3 mTorr and the supply d.c. poweris 800 W/100 mm diameter.

[0089] As shown in Table 3, the intermediate layers 13 of the magneticrecording media No. 1 to No. 4 had preferable mean grain sizes(diameters) and grain size distributions, reflecting those of theinorganic compound layer 2. Similarly, the magnetic layers 3 also hadpreferable mean grain sizes (diameters) and grain size distributions,reflecting those of the intermediate layers 13.

[0090] The intermediate layer 13 of FIG. 4(a) have its particles 17arranged regularly and separated from each other by grain boundaries 18.

[0091] The lattice constant of the intermediate layer 13 can becontrolled by the concentration of titanium Ti. By controlling the Ticoncentration so that the lattice constant of the intermediate layer 13may be between the lattice constant of the inorganic compound layer andthe lattice constant of the magnetic layer, we can grow the inorganiccompound layer, the intermediate layer, and the magnetic layer insequence more easily and more steadily.

[0092] The magnetic layer 3 of FIG. 4(a) has its magnetic particles 14arranged regularly and separated from each other by grain boundaries 15.

[0093] The magnetic recording medium No. 5 forms a magnetic layer 3, anintermediate layer 13 comprising crystal particles 17 and amorphousgrain boundary phases 19, and an inorganic compound layer 2 in sequenceon the substrate. (See FIG. 4(b). )

[0094] The intermediate layer 13 is formed by simultaneously sputteringa Cr (90 parts)—Ti (10 parts) alloy target which is the same as thoseused for formation of the intermediate layer of the magnetic recordingmedium No. 2 and a sintered target comprising one molar part of siliconoxide and one molar part of titanium oxide.

[0095] The magnetic layer 3 of the magnetic recording medium No. 5 wasprepared in the same manner as the magnetic layers of the magneticrecording media No. 1 to No. 4. This magnetic layer 3 has a better grainsize distribution than the magnetic layers of the magnetic recordingmedia No. 1 to No. 4.

[0096] The intermediate layer 13 of the magnetic recording medium No. 6was prepared in the same manner as the intermediate layer of themagnetic recording medium No. 5. Further a magnetic layer 3 comprisingcrystal particles 14 and amorphous grain boundary phases 16 was formedon the intermediate layer 4. The magnetic layer 3 of FIG. 4 (c) has itsmagnetic particles 14 arranged regularly and separated from each otherby grain boundaries phase 16.

[0097] The magnetic layer 3 of the magnetic recording medium No. 6 isformed by simultaneously sputtering a Co—Cr—Pt alloy target which is thesame as those used for formation of the magnetic layers of the magneticrecording medium No. 1 to No. 4 and a sintered target comprising onemolar part of silicon oxide and one molar part of titanium oxide. Thismagnetic layer 3 of the magnetic recording medium No. 6 has a bettergrain size distribution than the magnetic layers of the magneticrecording media No. 1 to No. 4.

[0098] A magnetic layer 3 of the magnetic recording medium 7 comprisingcrystal magnetic particles and amorphous grain boundary phases isdirectly formed on the inorganic compound layer 2 without theintermediate layer.

[0099] The magnetic layer 3 of FIG. 4(d) has its magnetic particles 14arranged regularly and separated from each other by grain boundariesphase 16.

[0100] The magnetic layer 3 of the magnetic recording medium No. 7 wasprepared in the same manner as the magnetic layer of the magneticrecording media No. 6. This magnetic layer 3 of the magnetic recordingmedium No. 7 has a better grain size distribution than the magneticlayers of the magnetic recording media No. 1 to No. 4.

[0101] From close TEM observation of surfaces and sections of the layersformed of the magnetic recording media No. 1 to No. 7 in Table 1 , wefound epitaxial growth of the intermediate layers 13 and the magneticlayers 3 on the inorganic compound layers 2. Magnetic recording media(such as No. 6 and No. 7) which form a magnetic layer 3 comprisingmagnetic particles and grain boundary phases 16 have a better grain sizedistribution.

[0102] Although this embodiment uses a Cr—Ti alloy material for theintermediate layer 13 to improve the matching between the inorganiccompound layer 2 and the magnetic layer 3, the similar effect can beobtained by an alloy containing additional Ti, V, Mo, Mn, B, or W in theCr component of the Cr—Ti alloy material.

[0103] The inorganic compound layer formed on the substrate can controlthe grain size and the grain size distribution of the intermediate layerformed on the inorganic compound layer. Further the grain size and thegrain size distribution of the intermediate layer can be improved byletting the intermediate layer comprise both a particle formingcomponent and a grain boundary phase forming component.

[0104] In other words, judging from this embodiment, we found that thegrain size and the grain size distribution of the magnetic layer can beimproved by formation of an inorganic compound layer and an intermediatelayer under the magnetic layer. Further the grain size and the grainsize distribution of the magnetic layer can be improved by letting themagnetic layer contain both a particle forming component and a grainboundary phase forming component.

Embodiment 5

[0105] For this embodiment, magnetic disks No. 1 to No. 12 (see Table 4)were produced.

[0106] We prepared targets as explained below to form inorganic compoundlayers of magnetic disks No. 1 to No. 12.

[0107] We mixed cobalt oxides of mean grain size of 2.3 μm and 3.2 μmand Na₂O—SiO₂—CaO glass or a mixture of finest SiO₂ and TiO₂ (at a molarratio of 1:1) at a rate shown in Table 4, added ethyl alcohol to themixture to make a uniform slurry, dried the slurry into pellets by aspray dryer, pressure-shaped the pellets, hot-pressed and sintered thepressed material. We used the resulting materials as targets.

[0108] We sputtered each target by a high frequency power into aninorganic compound layer of 30 nm thick. Table 4 lists the crystalstatus, mean grain size, standard deviation/mean grain size, andcomposition of each inorganic compound layer.

[0109] Further we formed a 10 nm-thick magnetic layer(Co:Cr:Pt=69:19:12) on each inorganic compound layer, assembled theresulting recording media (magnetic disks) in a magnetic disk unit,wrote data equivalent to 20 Gbit/inch², read the data, and measured theS/N ratio (in dB). See Table 4. TABLE 4 Quantity of CoO in inorganic S/Nratio compound layer of magnetic No. Target composition (wt %) particles(wt %) Layer characterristics of inorganic compound layer disk (dB)Remarks 1 CoO: 99.5 Na₂O—SiO2—CaO 99 Particle: CoO crystal Grainboundary: 12 Comparative glass: 0.5 Mean grain size: 17.0 nm Amorphousexample Standard deviation/mean grain Grain boundary width: size × 100:29% <0.1 nm 2 CoO: 98.5 Na₂O—SiO2—CaO 98 Particle: CoO crystal Grainboundary: 25 — glass: 1.5 Mean grain size: 12.0 nm Amorphous Standarddeviation/mean grain Grain boundary width: size × 100: 18.2% <0.1 nm 3CoO: 95 Na₂O—SiO2—CaO 94.5 Particle: CoO crystal Grain boundary: 32 —glass: 5 Mean grain size: 11.2.0 nm Amorphous Standard deviation/meangrain Grain boundary width: size × 100: 17.5% <0.5 nm 4 CoO: 90Na₂O—SiO2—CaO 90 Particle: CoO crystal Grain boundary: 35 — glass: 10Mean grain size: 11.0 nm Amorphous Standard deviation/mean grain Grainboundary width: size × 100: 16.1% <0.7 nm 5 CoO: 85 Na₂O—SiO2—CaO 84.2Particle: CoO crystal Grain boundary: 34 — glass: 15 Mean grain size:10.2.0 nm Amorphous Standard deviation/mean grain Grain boundary width:size × 100: 15.2% <1.2 nm 6 CoO: 70 Na₂O—SiO2—CaO 67 Particle: CoOcrystal Grain boundary: 29 — glass: 30 Mean grain size: 7.2.0 nmAmorphous Standard deviation/mean grain Grain boundary width: size ×100: 14.2% <1.8 nm 7 CoO: 65 Na₂O—SiO2—CaO 63 Particle: CoO crystalGrain boundary: 11 Comparative glass: 45 Mean grain size: 6.0.0 nmAmorphous example Standard deviation/mean grain Grain boundary width:size × 100: 26.3% <2.9 nm 8 CoO: 95 SiO₂ + TiO₂: 5 95.1 Particle: CoOcrystal Grain boundary: 27 — Mean grain size: 13.2.0 nm AmorphousStandard deviation/mean grain Grain boundary width: size × 100: 16.2%<0.7 nm 9 CoO: 90 SiO₂ + TiO₂: 10 89.6 Particle: CoO crystal Grainboundary: 35 — Mean grain size: 12.0 nm Amorphous Standarddeviation/mean grain Grain boundary width: size × 100: 13.3% <0.9 nm 10CoO: 85 SiO₂ + TiO₂: 15 85.3 Particle: CoO crystal Grain boundary: 33 —Mean grain size: 12.0 nm Amorphous Standard deviation/mean grain Grainboundary width: size × 100: 16.2% <1.1 nm 11 CoO: 80 SiO₂ + TiO₂: 2080.1 Particle: CoO crystal Grain boundary: 28 — Mean grain size: 10.0 nmAmorphous Standard deviation/mean grain Grain boundary width: size ×100: 13.1% <2 nm 12 CoO: 65 SiO₂ + TiO₂: 45 62.5 Particle: AmorphousGrain boundary: 14 Comparative Mean grain size: 4.2 nm Amorphous exampleStandard deviation/mean grain Grain boundary width: size × 100: 26.3%<2.7 nm

[0110] The magnetic disk made of target composition No. 1 in Table 4contains 99% by weight CoO in the particles of the inorganic compoundlayer and features smaller grain bondary phase width, greater particlesin the inorganic compound layer, greater “Standard deviation (σ)/grainsize ×100” value and greater particles in the magnetic layer. Theresulting S/N ratio of the magnetic disk No. 1 is low.

[0111] The magnetic disk made of target composition No. 7 in Table 4contains 63% by weight CoO in the particles of the inorganic compoundlayer. The particles in the inorganic compound layer are extremely smalland far less crystallized. Therefore, the particles in the magneticlayer are hard to be controlled by the grain characteristics of theinorganic compound layer and the resulting S/N ratio of the magneticdisk No. 1 is low.

[0112] The magnetic disk made of target composition No. 10 in Table 4adds SiO₂ and TiO₂ instead of the Na₂O—SiO₂—CaO glass to the maincomponent CoO. We found that the components added to CoO will not changethe layer characteristics.

[0113] From Table 4, we can easily understand that the S/N ratio of aninorganic compound layer is 25 or above when the particles in theinorganic compound layer contains 65% to 98% by weight CoO. (Forexample, see target compositions No. 2 to No. 6 and Mo. 8 to No. 11.)

[0114] Therefore, the target should preferably contain 65% to 98% byweight CoO to get inorganic compound layers having such layercharacteristics.

[0115] Further, the width of a grain boundary phase in the inorganiccompound layer can be controlled by the ratio of the grain boundaryphase material in the target composition. When the width of the grainboundary phase is 0.1 nm to 2 nm, we can get an optimum distance betweenmagnetic particles in the magnetic layer and reduce the interaction ofmagnetic particles in the magnetic layer. The resulting magnetic diskhas a greatly-reduced unit of inversion of magnetization for recordingand deletion.

[0116] This embodiment uses target compositions of “CoO andNa₂O—SiO₂—CaO glass” and “CoO and SiO₂ plus TiO₂,” but cobalt oxide CoOcan be substituted by an oxide having the NaCl or spinel type crystalstructure. Similarly, the Na₂O—SiO₂—CaO glass or SiO₂ plus TiO₂ can besubstituted by oxides, nitrides, or borides of elements belonging toGroups I to V of the periodic table to get the similar effect.

[0117] As explained above, we can control particle materials, grainboundary phase materials, concentrations (rates of components), layerorientations, particle sizes (diameters), grain boundary phasethickness, and grain size distribution of each layer (inorganic compoundlayer, intermediate layer, and magnetic layer) by selecting materials orchanging conditions of layer formation. Crystal particles in each layershould preferably be so oriented that the lattice constants of theparticles may be matched easily.

[0118] The glass used as substrates 1 in this embodiment can besubstituted by high molecular materials such as polyethylene, polyester,polyolefin, cellulose, polyvinyl chloride, polyimide, and polycarbonate,metallic materials such as aluminum, aluminum alloy, and titanium alloy,ceramics glass such as aluminum glass, or composite materials of these.The substrate shapes can be any of disk, tape, film, sheet, card, anddrum.

[0119] There are two ways of recording information on the magneticrecording media: recording along the surface of the magnetic recordingmedium and recording perpendicularly to the surface of the magneticrecording medium.

[0120] The magnetic recording medium for recording along the surfaceuses cobalt alloy or the like of the hexagonal close-packed structure.The cobalt alloy layer has a one-axis anisotropy with the “c” axis as amagnetizable axis, the “c” axes are oriented along the surface of thelayer.

[0121] Similarly, the magnetic recording medium for recording verticalto the surface uses cobalt alloy or the like of the hexagonalclose-packed structure and the “c” axes are oriented vertically to thesurface of the layer. The orientation of the axis in the magnetic layercan be controlled also by formation of an inorganic compound layer or anintermediate layer formed between the inorganic compound layer and themagnetic layer. Therefore, the present invention is applicable to bothof the above recording ways.

[0122] The present invention has an effect of making crystal particlesin the magnetic layer fine and uniform fit for high-density recording:

What we claim is:
 1. A magnetic recording medium comprising: asubstrate; a plurality of information-recording magnetic layerslaminated on said substrate; and an inorganic compound layer containingcrystal particles and amorphous grain boundary phases surrounding saidparticles between said substrate and said magnetic layers; wherein saidmagnetic layers contains crystal magnetic particles whose mean grainsize is 4 nm to 15 nm and the standard deviation (σ) of the grain sizeis 25% or less of said mean grain size.
 2. A magnetic recording mediumcomprising: a substrate; a plurality of information-recording magneticlayers laminated on said substrate; and an inorganic compound layercontaining crystal particles and amorphous grain boundary phasessurrounding said particles between said substrate and said magneticlayers; wherein said magnetic layers contains crystal magnetic particlesand amorphous grain boundary phases surrounding said particles whosemean grain size is 4 nm to 15 nm and the standard deviation (σ) of thegrain size is 25% or less of said mean grain size.
 3. A magneticrecording medium comprising: a substrate; a plurality ofinformation-recording magnetic layers laminated on said substrate; andan inorganic compound layer containing crystal particles and amorphousgrain boundary phases surrounding said particles between said substrateand said magnetic layers; wherein said inorganic compound layercomprises a first component containing sodium chloride (NaCl) or spineltype crystal oxide and a second component containing oxide, nitride, orboride of elements belonging to Groups I to V of the periodic table andwherein said particles and said grain boundary phase both contain saidfirst and second components and said particles contain more firstcomponent than said grain boundary phase.
 4. A magnetic recording mediumaccording to claim 3, wherein said particle contains 65% to 98% byweight of an oxide which is the first component and 35% to 2% by weightof oxide, nitride, or boride which is the second component and saidgrain boundary phase contains 50% to 90% by weight of an oxide which isthe first component and 50% to 10% by weight of oxide, nitride, orboride which is the second component.
 5. A magnetic recording mediumaccording to claim 3, wherein the sodium chloride (NaCl) type crystaloxide is cobalt oxide (CoO), ferric oxide (Fe₂O₃), magnesium oxide,manganese oxide, titanium oxide, copper oxide or nickel oxide.
 6. Amagnetic recording medium according to claim 3, wherein the spinel typecrystal oxide is cobalt oxide (Co₃O₄) or ferrous oxide (Fe₃O₄).
 7. Amagnetic recording medium according to claim 3, wherein the mean grainsize, the standard deviation (σ) of grain size, the short diameter tolong diameter ratio of said particle, and the grain boundary phase widthare respectively 4 nm to 15 nm, 25% or less of said mean grain size, 0.7to 1.0 and 0.1 nm to 2 nm in that order.
 8. A magnetic recording mediumaccording to claim 3, wherein said magnetic layers are made of alloycontaining cobalt.
 9. A magnetic recording medium according to claim 3,wherein said magnetic layers comprise crystal magnetic particles andamorphous grain boundary phases surrounding said magnetic particles. 10.A magnetic recording medium according to claim 3, wherein said grainboundary phase contains oxide, nitride, or boride of elements belongingto Groups I to V of the periodic table.
 11. A magnetic recording mediumaccording to claim 3, further comprising an intermediate layer betweensaid inorganic compound layer and said magnetic layers; wherein saidintermediate layer contains crystal particles whose mean grain size is 4nm to 15 nm and the standard deviation of the grain size (σ) is 25% orless of said mean grain size.
 12. A magnetic recording medium accordingto claim 11, wherein said intermediate layer comprises crystalCr-related metal particles and amorphous grain boundary phasessurrounding said magnetic particles in said intermediate layer.
 13. Amethod of manufacturing a magnetic recording medium comprising asubstrate, a plurality of information-recording magnetic layerslaminated on said substrate, and an inorganic compound layer betweensaid substrate and said magnetic layers; said inorganic compound layerbeing formed by the step of simultaneously sputtering a first targetcomprising sodium chloride (NaCl) or spinel type crystal oxide and asecond component comprising at least one of oxide, nitride, and borideof elements belonging to Groups I to V of the periodic table to formsaid inorganic compound layer.
 14. A method of manufacturing a magneticrecording medium comprising a substrate, a plurality ofinformation-recording magnetic layers laminated on said substrate, andan inorganic compound layer between said substrate and said magneticlayers; said inorganic compound layer being formed by the step ofsputtering a target which is a mixture of sodium chloride (NaCl) orspinel type crystal oxide and a compound comprising at least one ofoxide, nitride, and boride of elements belonging to Groups I to V of theperiodic table to form said inorganic compound layer.
 15. A method ofmanufacturing a magnetic recording medium comprising a substrate, aplurality of information-recording magnetic layers laminated on saidsubstrate, and an inorganic compound layer between said substrate andsaid magnetic layers; said magnetic layer inorganic compound beingformed by the step of simultaneously sputtering a first targetcomprising cobalt (Co), platinum (Pt) and at least one of chromium (Cr),tantalum (Ta), and niobium (Nb), and a second target comprising at leastone of oxide, nitride, and boride of elements belonging to Groups I to Vof the periodic table to form said magnetic layer.
 16. A method ofmanufacturing a magnetic recording medium comprising a substrate, aplurality of information-recording magnetic layers laminated on saidsubstrate, and an inorganic compound layer between said substrate andsaid magnetic layers; said magnetic layers being formed by the step ofsputtering a target which is a mixture of cobalt (Co), platinum (Pt), atleast one of chromium (Cr), tantalum (Ta), and niobium (Nb), and atleast one of oxide, nitride, and boride of elements belonging to GroupsI to V of the periodic table to form said magnetic layer.
 17. A magneticrecording unit using said magnetic recording medium according toclaim
 1. 18. A magnetic recording unit using said magnetic recordingmedium according to claim
 2. 19. A magnetic recording unit using saidmagnetic recording medium according to any of claim 3.